class Solution
{
public:
    bool CheckPermutation(string s1, string s2)
    {
        if (s1.size() != s2.size())
            return false;
        int hash[26] = {0};
        for (auto ch : s1)
            hash[ch - 'a']++;
        for (auto ch : s2)
        {
            hash[ch - 'a']--;
            if (hash[ch - 'a'] < 0)
                return false;
        }
        return true;
    }
};